Doctor for paper and like machines



March 30, 1954 H. E. B. SCOTT 2,673,494

DOCTOR FOR PAPER AND LIKE MACHINES Filed Nov. 29, 1951 s Shets-Sheet 1ff/wozo 5 50077 Mamh 1954 H. E. B. SCOTT DOCTOR FOR PAPER AND LIKEMACHINES 3 Sheets-Sheet 2 Filed Nov. 29 1951 March 30, 1954 H. E. B.SCOTT 2,673,494 DOCTOR FOR PAPER AND LIKE MACHINES Filed Nov. 29, 1951 3Sheets-Sheet 3 155420.40 E5? corr Patented Mar. 30, 1954 2,673,494DOCTOR FOR PAPER AND LIKE MACHINES Harold Eric Baliol Scott, Weybridge,

England Application November 29, 1951, Serial N 0. 258,850

8 Claims.

This invention relates to doctors for paper making and other machinesincluding rolls or cylinders which have to be kept clean, e. g. boardmaking machines, pulp making machines, milk dryers, metal foil rollingmills, and glueing, creping or combining machines.

More specifically, the invention relates to that type of doctor whichcomprises a holder and a thin blade which is a loose fit in alongitudinal retaining recess in the holder irregularity in the surfaceof the roll, the holder being biassed, by gravity or springs, so as tomaintain the blade Owing to the necessity for a loose fit between theblade and its holder, trouble has been experienced due to the bladesfalling out of the holder,

recess in the holder. While this overcomes one trouble it introduces wayinto the blade-retaining recess in the holder, particularly on doctorsfitted to rolls at the wet end of the paper making machine where thefibres are in the form of slurry, with the result that the blade becomesfast in its holder, and great difiiculty is often experienced inremoving a worn blade longitudinally from the retaining process. Thetime occupied in changing a difiicult blade means great loss inproduction.

To obviate this difliculty, it has been proposed in Patent No. 2,077,816to provide slots in the front wall of the retaining recess, so that theblade may be removed laterally from the front of the holder by merelysliding the blade a short distance longitudinally until the retainingprojections on the blade are opposite the slots. In that patent it hasalso been proposed to provide members which normally look the blade inits retaining recess, but can be freed, by sliding or rotationalmovement in relation to the holder, to release the blade so that it canbe removed laterally from the retaining groove.

In many cases the doctor has to be located in such a position that it isnot possible to fit a new blade laterally from the front of the doctor,although a worn blade is, therefore, necessary-if the doctor is to betruly universal-for the blade to be capable of being fitted and alsoremoved both longitudinally from the end and also laterally from thefront of the holder.

In all previously proposed doctors having blade retaining means, theblade retaining recess has been located below the bottom surface of theblade, i. e. the side of the blade facing the roll.

in contact with the roll. Y

can be thus removed. It i While, throughout this specification, thesurface 60 longitudinally,

of the blade facing the roll is referred to as its bottom surface andits other surface as its top surface, it will be appreciated that doctorblades are in many instances mounted beneath the roll, so that itsbottom surface is, in space, located above its top surface. There isalways a tendency for fibres and other matter in the paper pulp toaccumulate on the bottom surface of the doctor blade behind the trailingedge of the portion of the blade which is in contact with the roll andthe blade retaining recess is accordingly exposed to this pulp. Also, asthe blade pivots or bends from its back edge when pressure is applied tothe doctor it lifts away from the front lip of the blade retainingrecess with the result that a gap is left between the blade and thefront edge of the recess through which pulp can gain access to and chokeup the blade retaining mechanism.

The present invention provides a doctor of the above type, comprising aretaining member within the recess in the holder which is free to pivotin the holder about a longitudinal axis and has a groove accommodatingthe rear end of the blade, the rear edge of the blade being locatedbehind said pivotal axis so that, when the blade is in working positionon the roll it will rock the retaining member in a direction such thatthe bottom surface of the blade seals the front end of the groove, andthe blade having projections which coaot, either with the retainingmember or with the holder, to prevent lateral removal of the blade whenin Working position but which can be freed, by pivotal movement of theretaining member in relation to the holder after the blade has beenlifted off the roll, to permit of lateral removal of the blade.

The blade can thus be removed at will either or laterally without anylongimovement in relation to the To allow of lateral withdrawal of thetudinal sliding holder.

blade it is only necessary to lift the blade off the roll and to turnthe retaining member in relation to the holder until the projections onthe blade are freed.

In the preferred form of doctor according to the invention the retainingmember is constituted by a cylindrical retaining rod mounted in therecess in the holder for rotation about its longitudinal axis and havinga blade retaining groove, the blade being disposed in the groove withits rear edge behind the longitudinal axis of the rod Preferably, theblade has projections on top surface which coact with a forwardlyprojecting lip on the holder, so as normally to prevent lat eral removalof the blade, but which can be moved clear of the lip, after the bladehas been lifted off the roll, by rotation of the rod in relation to theholder. Alternatively, however, the blade may have projections on itsundersurface which coact with the front edge of the groove in the blade21 and the retaining member to prevent lateral removal of the blade whenit is in working position. When, however, the blade has been lifted offthe roll, its upper surface can be moved, by rotation of the rod, awayfrom the holder to a position in which the projections can be leveredout of the groove in the retaining member, so freeing the blade forlateral removal.

Various embodiments of doctor according to the invention will now bedescribed in detail, by way of example, with reference to theaccompanying drawings, in which:

Fig. l is a front elevation of one form tor, showing it applied to aroll in a paper machine,

Fig. 2 is an enlarged the doctor shown in Fig. 1,

Fig. 3 is a sectional view through a doctor of the kind shown in 2 andillustrating a device for latching the blade against removal,

Fig. a is a corresponding plan view,

Figs. 5 and G are views similar to Fig. 3, illustrating how the blademay be removed,

Fig. '2 is an end View of a doctor of the kind shown in Fig. 2 andfitted with an alternative form of latching device,

Figs. 8 and 9 are corresponding plan views, with the latch inalternative positions,

Figs. 10-13 are sectional views tive forms of doctors,

Fig. 14 is a sectional view through a doctor generally similar to thatof 2 but with a built-up holder, and

Fig. 15 is a perspective view of a sectional. taining rod.

Like reference characters designate like parts throughout the figures.

Referring first to Figs. 1 and 2, the holder 26 of the doctor isconstituted. by an extruded. section which extends along the entirelength of the roll ii to which the doctor is fitted. The holder has apart cylindrical recess 22 in its front face, i. e. the face nearer theroll. In the recess 2?. is accommodated a cylindrical retaining rod 23having in it a blade retaining groove 24 formed with a flat surface 25against which rests the rear edge 25 of the blade 2'1. As is clear fromFig. 2 the rear edge 26 of the blade is located behind the center of therod 23. The holder 2% is mountof docmaking sectional view throughthrough alternaed on a bar 28 (Fig. 1) carried by an angle sectionsupport 23 which is mounted on a rod 3!}, and gravity maintains theblade 21 in contact with the roll 21. Projections 3| on the top surfaceof the blade extend upwardly into the groove 24 in the rod 23 and a lip32 on the front of the holder 26 coacts with the projections 3i toprevent lateral removal of the blade 2? so long as the latter ispressing on the roll 2 l. The forward end 33 of the holder is extendedbeyond the lip 32 to provide a continuous longitudinal support for thetop surface of the blade 21 between its front and rear edges.

The blade 21' is free to slide lengthwise in the groove 24 in the rod23, means described later being provided to hold the blade againstendwise removal from the rod during normal operation. The operatingpressure on the blade 2'! keeps the projections 3| on the blade in aposition such that accidental lateral movement of the blade out of theholder is impossible and excessive pressure on the blade cannot forcethe blade out of the holder as is the case in some previously proposeddoctors. The open part 2441 of the blade retaining groove in the rod 23is located above the top surface of is therefore shielded from the pulpwhich accumulates behind the trailing edge of the blade. This pulpcannot enter the portion of the groove 24 beneath the blade because thepressure of the blade, due to the location of its rear edge 25 behindthe center of the rod 23, tends to rotate the rod in a counterclockwisedirection, thereby ensuring that the flat surface 34 at the front of thegroove 24 is firmly pressed against the bottom surface of the blade. Theforward extension 33 of the holder shields the retaining groove 24 inthe rod from pulp which may accumulate on the top surface of the blade21.

The blade 21 can be inserted or removed either from the end or the frontof the doctor, as desired.

The advantages of the doctor shown in Figs. 1 and 2 are as follows:

(1) Should the blade retaining groove 24, notwithstanding that it iswell shielded, become choked with pulp, the blade 2'! can easily beremoved laterally from the doctor and without any longitudinal movement.

(2) There is no possibility of excessive pressure on the blade 2'!springing the blade out of its retaining groove 24. As the rear edge 26of the blade is behind the center of the rod, the pressure on the bladetends to rotate the rod in the direction to keep the retaining grooveclosed and to ensure that the projection 3| on the blade cannot pass thelip 32 on the holder.

(3) Various thicknesses of blades can be used by replacing only theround blade-retaining rod 23 by another having a suitable size of slot.There is no need to change the holder 26.

(4) After a period of use, the thrust of the rear edge 26 of the bladewears away its support. It is then only necessary to fit a new retainingrod 23, and not to replace the holder 2! as in the case of the knowntypes of doctor.

5) The blade retaining groove 24 is at all times shielded from contactwith pulp and liquid.

In Figs. 3-6 is shown one form of latch for holding the blade 21 againstremoval from the rod 23 during normal operation. One end of the groove24 in the rod is closed. Into the other end of the rod is fitted a screw31, the shank 35 of which extends through a circumferential slot 38 inthe holder 23. When the screw 31 is screwed home, as shown in Fig. 3,its threaded end 35 prevents endwise removal of the blade 21 from thegroove 24 in the rod 23. The shank 36 of the screw 31 can rotatecounter-clockwise in the slot 38 to allow of counter-clockwise rotationof the rod 23 and therefore of maintenance of the surface 34 in contactwith the undersurface of the blade 21. The shank 35 however coacts withthe left hand end of the slot 38 to prevent clockwise rotation of therod 23 to an extent sufficient to clear the projections 3| from the lip32. The blade 21 cannot therefore be removed laterally from the groove24.

When the screw 31 is partially unscrewed, as shown in Fig. 5, itsthreaded end 35 is brought below the blade 21, so that the blade can beremoved endwise from the doctor, but the shank 36 still coacts with theslot 38 to prevent lateral removal of the blade.

When the screw 31 is further unscrewed to the position shown in Fig. 6,the thin threaded portion 35 thereof is brought into the slot 38 withthe result that, after lifting the blade 21 oil the roll 2|, the rod 23can rotate clockwise to a position in which the lip 32 no longerprevents lateral withdrawal of the blade.

An alternative form of latch is shown in Figs.

74?. As before, one end of the groove 24 in the rod 23 is closed and aremovable split pin 39 at the other end of the rod normally preventsendwise removal of the blade. A U-shaped clip 6!), hinged at 4! to anextension 42 of the rod can be moved to the position shown in Fig. 8, inwhich it engages the holder 25) to prevent rotation of the rod 23 in thedirection required for lateral removal of the blade. There is, however,sufficient clearance between the top limb of the clip 4! and the holder25 to allow of the small degree of counter-clockwise rotation of the rod23 necessary to ensure that-the surface 34 will bear against theundersurface of the blade 27. When the clip is swung to the positionshown in Fig. 9, the rod 23 is freed for clockwise rotation to theposition in which the blade may be with drawn laterally.

If desired, instead of closing one end of the recess 24 in the rod 23,latches such as those shown in Figs. 3-6 or in Figs. 7-9 may be providedat both ends of the rod.

In the doctor shown in Fig. 10, the forward extension of the holder isreplaced by a spring plate 43, which may be straight, or curved asshown, and which presses against the top surface of the blade 21throughout its length and the rear edge of which is accommodated in aretaining groove 44 in the holder and provided with projections 45 whichprevent lateral removal of the spring plate M from the holder.

In Fig. 13 is shown a doctor in which the retaining member I23 is not acylindrical rod but is of approximately \l-section, and is mounted torock on a projection 47 at the base of the recess 22 in the holder 20.

The holder of the doctor shown in Fig. 14 is of built-up constructionand not extruded. It can consequently be made of steel and other metalswhich cannot be extruded, and is of special utility having regard to thepresent shortage both of extruded sections and of non-ferrous metals.The body portion I20 of the holder is machined from bar and the base ofthe opening 22 in the holder is closed by a bar 220 welded or otherwisesecured to the member 120. This construction has the advantage that theangle of presentation of the blade 21 to the roll is angle to which theinner face of the projection 33 is machined. Consequently, to constructdoctors with different blade presentation angles, it is only necessaryto provide members I20 with projections 33 machined at different anglesand Fig. 1) for the doctor.

If desired the rod, whether solid or of the sheet metal constructionjust described, can, as shown determined by the I in Fig. 15, beconstituted of several sections, such as 23a, 23b, 230, havinginterlocking ends with the result that the blade will be given extraflexibility.

I claim:

1. A doctor blade and blade holder assembly comprising, a blade holderhaving a longitudinal recess, a blade retaining member fitting saidrecess and free to pivot about a longitudinal axis, said member having ablade receiving longitudinal groove, a blade having its rear edge insaid blade having at least one projection, means operative in the activeposition of the blade to lock the blade against lateral removal of theblade from the blade retaining member, said means being disengaged fromsaid projection by pivotal movement of said retaining member about saidaxis to permit lateral removal of said blade from said retaining memberand said holder.

2. An assembly as set forth in claim 1 in which the blade holder recessis cylindrical and the blade retaining member is coaxial with saidrecess.

3. An assembly as set forth in claim 1 in which the blade holder has aforwardly projecting lip bearing on the blade and coacting with at leastone projection on the blade to prevent lateral removal of the blade.

at. A doctor as set forth in claim 1 in which the blade holder recess iscylindrical, the blade retaming member is coaxial with said recess andis formed of sheet metal, the metal extending forwardly from theretaining groove to form a spring plate bearing against the uppersurface of the blade.

5. The assembly as set forth in claim 1 wherein the retaining member isof approximately V-section and mounted in the recess and holder so thatit may rock about its base.

6. An assembly as set forth in claim 1 in which the retaining member isconstituted of several coaxial sections having interlocking ends.

'7. An assembly as set forth in claim 1 in which the blade retainingmember comprises a cylindrical rod mounted in the recess in the bladeholder, said rod having a blade retaining groove, at least one end ofthe rod having a projecting member for engaging a slot in the bladeholder, said projection being adjustable from a locking position .tosuccessive positions in the first of which it frees the blade forendwise withdrawal and in the second of which it also frees the bladefor lateral withdrawal.

8. An assembly as set forth in claim 1 having at least one end of theblade retaining member a clip pivoted to an extension of the bladeretaining member and engageable with the blade holder to preventpivoting of the blade retaining member in such direction as to enablelateral withdrawal of the blade.

HAROLD ERIC BALIOL SCOTT.

References Cited in the file of this patent UNITED STATES PATENTS

